US troops will leave Syria for Western Iraq: Defence Secretary

File photo of US troops atop an armoured vehicle near the Syrian border rown of Ras al-Ayn | AFP

US Defence Secretary Mark Esper says that under current plans all US troops leaving Syria will go to western Iraq and the American military will continue to conduct operations against the Islamic State group to prevent its resurgence.

Esper, who arrived in the Afghan capital on Sunday, did not rule out the idea that US forces would conduct counterterrorism missions from Iraq into Syria. But he told reporters travelling with him that those details will be worked out over time.

His comments were the first to specifically layout where American troops will go as they shift from Syria and what the counter-IS fight could look like.

Esper, who flew overnight to Afghanistan, said he has spoken to his Iraqi counterpart about the plan to shift about 1,000 troops leaving Syria into western Iraq.

The developments made clear that one of President Donald Trump's rationales for withdrawing troops from Syria was not going to come to pass any time soon.

"It's time to bring our soldiers back home," Trump said Wednesday.

They are not coming home, although Trump tweeted Sunday: "USA soldiers are not in combat or ceasefire zones" and "Bringing soldiers home!"

As Esper left Washington on Saturday, US troops were continuing to pull out of northern Syria after Turkey's invasion into the border region.

Reports of sporadic clashes continued between Turkish-backed fighters and the US-allied Syria Kurdish forces despite a five-day cease-fire agreement hammered out Thursday between US and Turkish leaders.

Turkey's defence ministry said one soldier has been killed amid sporadic clashes with Kurdish fighters.

Trump ordered the bulk of the approximately 1,000 US troops in Syria to withdraw after Turkish President Recep Tayyip Erdogan made it clear in a phone call that his forces were about to invade Syria to push back Kurdish forces that Turkey considers terrorists.

The pullout largely abandons America's Kurdish allies who have fought IS alongside U.S. troops for several years.

Between 200 and 300 U.S. troops will remain at the southern Syrian outpost of Al-Tanf.

Esper said the troops going into Iraq will have two missions.

"One is to help defend Iraq and two is to perform a counter-ISIS mission as we sort through the next steps," he said.

"Things could change between now and whenever we complete the withdrawal, but that's the game plan right now."

The US currently has more than 5,000 American forces in Iraq, under an agreement between the two countries.

The US pulled its troops out of Iraq in 2011 when combat operations there ended, but they went back in after IS began to take over large swaths of the country in 2014.

The number of American forces in Iraq has remained small due to political sensitivities in the country, after years of what some Iraqis consider US occupation during the war that began in 2003.

Esper said he will talk with other allies at a NATO meeting in the coming week to discuss the way ahead for the counter-IS mission.

Asked if US special operations forces will conduct unilateral military operations into Syria to go after IS, Esper said that is an option that will be discussed with allies over time.

He said one of his top concerns is what the next phase of the counter-IS missions looks like, "but we have to work through those details. He said that if US forces do go in, they would be protected by American aircraft.

While he acknowledged reports of intermittent fighting despite the cease-fire agreement, he said that overall it "generally seems to be holding. We see a stability of the lines, if you will, on the ground."

He also said that, so far, the Syrian Democratic Forces that partnered with the US to fight IS have maintained control of the prisons in Syria where they are still present. The Turks, he said, have indicated they have control of the IS prisons in their areas.

"I can't assess whether that's true or not without having people on the ground," said Esper.

He added that the US withdrawal will be deliberate and safe, and it will take "weeks not days." According to a U.S. official, about a couple hundred troops have left Syria so far. The U.S. forces have been largely consolidated in one location in the west and a few locations in the east.

The official, who spoke on condition of anonymity to discuss ongoing operations, said the US military is not closely monitoring the effectiveness of the cease-fire, but is aware of sporadic fighting and violations of the agreement. The official said it will still take a couple of weeks to get forces out of Syria.

Also Sunday, US House Speaker Nancy Pelosi led a group of American lawmakers on a visit to Jordan to discuss "the deepening crisis" in Syria.

Jordan's state news agency Petra said that King Abdullah II, in a meeting with the Americans, stressed the importance of safeguarding Syria's territorial integrity and guarantees for the "safe and voluntary" return of refugees.